Ju Hyung We

A wearable thermoelectric generator fabricated on a glass fabric

The conversion of body heat into electrical energy using a thermoelectric (TE) power generator is useful for wearable self-powered mobile electronic systems such as medical sensors or smart watches. We herein demonstrate a glass fabric-based flexible TE generator using a screen printing technique and the self-sustaining structure of a TE device without top and bottom substrates. With this technique it is possible to make the device thin (∼500 μm), lightweight (∼0.13 g cm−2), and flexible. In addition, the developed TE generator achieved an unprecedentedly large output power density which is several tens of times higher than that of flexible TE generators reported to date. The developed TE generator shows an allowable bending radius of as low as 20 mm and no change in performance by repeated bending for 120 cycles. This work can expedite the development of wearable self-powered mobile devices.

High-Performance Flexible Thermoelectric Power Generator Using Laser Multiscanning Lift-Off Process

Flexible thermoelectric generators (f-TEGs) are emerging as a semipermanent power source for self-powered sensors, which is an important area of research for next-generation smart network monitoring systems in the Internet-of-things era. We report in this paper a f-TEG produced by a screen-printing technique (SPT) and a laser multiscanning (LMS) lift-off process. A screen-printed TEG was fabricated on a SiO2/a-Si/quartz substrate via the SPT process, and the LMS process completely separated the rigid quartz substrate from the original TEG by selective reaction of the XeCl excimer laser with the exfoliation layer (a-Si). Using these techniques, we fabricate a prototype f-TEG composed of an array of 72 TE couples that exhibits high flexibility at various bending radii, together with excellent output performance (4.78 mW/cm2 and 20.8 mW/g at ΔT = 25 °C). There is no significant change in the device performance even under repeated bending of 8000 cycles.

Simultaneous measurement of the Seebeck coefficient and thermal conductivity in the cross-sectional direction of thermoelectric thick film

The measurement of the thermoelectric properties of thin film thermoelectric materials has been an issue due to the difficulty and inaccuracy. In this work, we present a new model to simultaneously extract the Seebeck coefficient and thermal conductivity in the cross-sectional direction of thin film thermoelectric material. The proposed method uses a sandwich structure composed of a metal electrode/TE film/metal electrode and measures the external Seebeck coefficient at two different intervals on the metal electrode. A theoretical model enables us to extract the Seebeck coefficient and thermal conductivity of the thermoelectric material from the two external Seebeck coefficient measurement values. The proposed method is applied to screen-printed ZnSb film with copper electrodes and the measurement results were found to lie in a reasonable range. Given that this method is simple to use, it will contribute to the development of thin film thermoelectric devices.

Enhanced thermoelectric properties of screen-printed Bi0.5Sb1.5Te3 and Bi2Te2.7Se0.3 thick films using a post annealing process with mechanical pressure

A cost-effective and large-scale thermoelectric (TE) energy harvester is becoming increasingly important for energy recovery systems such as self-powered electronics and renewable power generation. Here, we report on a TE device composed of p-type Bi0.5Sb1.5Te3 and n-type Bi2Te2.7Se0.3 TE materials prepared using a screen-printing process, which has the advantages of low cost, scalability to large areas and the ability to form a flexible TE generator. The TE properties of the screen-printed TE thick films were optimized via subsequent annealing with mechanical pressure. It was found that thermal annealing with the application of mechanical pressure plays a key role in controlling the carrier concentration and improving the density of the TE thick films. Under optimized annealing conditions, the Bi0.5Sb1.5Te3 (p-type) thick film had a ZT of 0.89 and a density of 5.67 g cm−3 while the Bi2Te2.7Se0.3 (n-type) thick film had a ZT of 0.57 and a density of 5.68 g cm−3 at room temperature. TE generators composed of 72 and 200 couples were fabricated with these thick films. The output power of the device composed of 72 couples was 0.1 W for a temperature difference (ΔT) of 28 K. Another device with 200 couples generated 0.31 W of electric power for the same ΔT.